CAIRO (AP) — Egypt’s worst violence in months escalated the confrontation between political forces and the ruling military ahead of a landmark presidential election, as suspected army supporters attacked mainly Islamist protesters outside the Defense Ministry Wednesday, sparking clashes that left at least 11 people dead.

Political parties swiftly blamed the ruling generals for the bloodshed and vowed the election must go ahead as planned to ensure the military’s removal from power.

Egypt has been plagued by sporadic bouts of deadly violence since the ouster of longtime authoritarian leader Hosni Mubarak last year, but Wednesday’s killings took on added significance, coming just three weeks ahead of the presidential election. The killings also provided opponents of the military with more evidence the generals who took over from Mubarak are badly bungling the shift to democratic rule and acting much like their former mentor.

“We blame the military council for the bloodshed,” Islamist lawmaker Osama Yassin of the Muslim Brotherhood’s Freedom and Justice Party told state television.

Around 1,000 protesters have been camped outside the Defense Ministry for days demanding an end to military rule. Most are supporters of disqualified presidential candidate Hazem Salah Abu Ismail, an ultraconservative Islamist barred from running because his late mother held dual Egyptian-U.S. citizenship, making him ineligible under election laws.

But the violence, which broke out at dawn, prompted other factions to join in. Throughout the day, thousands marched to the site of the clashes in the Cairo district of Abbasiyah, protesting into the evening surrounded by armored vehicles and lines of riot police.

The fundamentalist Brotherhood, Egypt’s strongest movement, quickly moved to try to reap political gains from what has turned into a growing confrontation between it and the military. In a statement, it held the military responsible and warned that Egyptians would show “no mercy” if the generals did not meet what it called the revolution’s demands.

The Brotherhood urged a new mass protest on Friday in Cairo’s Tahrir Square to ensure the military hands over power by July 1 as promised.

The Brotherhood has been frustrated that its domination of parliament — where it holds nearly half the seats — has not translated into political power because the military has kept executive rule in its own hands.

Their increasingly bitter quarrel has centered on the military-backed government led by Prime Minister Kamal el-Ganzouri. The Brotherhood has demanded that the military dismiss the government and allow the Islamist majority in parliament to form a new one. The generals have so far ignored the calls, and in response Parliament Speaker Saad el-Katatni, a Brotherhood leader, suspended the chamber’s sessions for a week on Sunday in protest.

The Brotherhood was also dealt a severe blow when a court last month suspended a 100-member panel formed by parliament to draft a new constitution. The panel was dominated by the Brotherhood and other Islamists, and the generals are pushing lawmakers to come up with an acceptable method of selection for a new panel.

The Brotherhood’s party leader, Mohammed Morsi, is one of three front-runners in the presidential race, along with former foreign minister Amr Moussa and a moderate Islamist, Abdel-Moneim Abolfotoh. The first round of voting is set for May 23-24.

But many fear the military will try to retain a say in politics even after handing over power to the election winner.

Seeking to allay fears the military might push back the handover and cling to power, Chief of Staff Gen. Sami Anan said the military was ready to step down if the election produces an outright winner — a highly unlikely scenario. None of the 13 candidates is expected to secure at least 50 percent of the vote, meaning a runoff between the top two contenders is likely on June 16-17.

To protest Wednesday’s violence, several presidential candidates temporarily suspended their campaigns. Several key political parties, including the Brotherhood, also boycotted a meeting with the generals.

“It is not possible for us to talk now, while blood is being shed just meters away,” said Essam el-Erian, a senior figure in the Brotherhood’s political party.

Nevertheless, the ruling military council met with the other political factions to discuss efforts to create a new constitutional panel.

The violence also led to the cancellation of the first presidential debate, between Moussa and Abolfotoh, which had been scheduled for nationwide broadcast Thursday night.

In many ways, Wednesday’s clashes were a repeat of previous violence over the 14 months since Mubarak’s ouster — a peaceful, anti-military demonstration set upon by armed men as police or army troops looked on without intervening.

On Wednesday, the army and police did not move for hours to separate the two sides.

Of the 11 killed, nine died of gunshots to the head and two suffered stabbing wounds, according to medical officials and police reports. The gunshots to the head suggested sniper fire.

Theories of who is behind the attacks of the past year have varied, with many activists blaming plainclothes police, army troops or petty criminals working for the police. Others spoke of hard-core Mubarak loyalists or thugs hired by Mubarak-era businessmen who have been hurt by the overthrow of the regime.

Abbasiyah residents and the protesters traded accusations of tit-for-tat attacks and intimidation.

“Salafis attacked us and our houses. They sealed off our streets, checking our IDs and damaging our shops and pharmacies. We were afraid. I am forced to arm myself,” said one resident, driver Essam Bakheit. “They say we are thugs but I swear we are not. I was born here. They are liars.”

Mohammed Fathi, a bearded Abu Ismail supporter, said the protesters did not instigate the violence. “Every night since we held our first day of protest, thugs climb the bridge above us and shower us with bombs and gunshots,” he said.

The clashes broke out at dawn when assailants set upon several hundred protesters, security officials and witnesses said. The clashes resumed later in the morning, but then stopped again when lines of black-clad riot police and army troops backed by armored vehicles finally moved in to separate the two sides at noon.

“The army’s intervention has come hours too late,” Amnesty International spokesman Philip Luther said in a statement. “There appears to be no will within Egypt’s ruling Supreme Council of the Armed Forces to prevent these tragic events.”

Sami Mahmoud, a 42-year-old Abbasiyah resident, said he was standing guard outside his building early Wednesday when a group of armed men roamed the streets shooting in the air and at balconies.

“Nobody protected us. The military and police didn’t intervene. They let us down,” he said.